Network Working Group R. Shoemaker
Internet-Draft ISRG
Intended status: Standards Track March 27, 2017
Expires: September 28, 2017
ACME IP Identifier Validation Extensiondraft-shoemaker-acme-ip-00
Abstract
This document specifies identifiers and challenges required to enable
the Automated Certificate Management Environment (ACME) to issue
certificates for IP addresses.
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{"type": "ip", "value": "2001:db8::1"}
4. Identifier Validation Challenges
When creating an authorization for a identifier with the type "ip"
the following challenge types MAY be used to perform validation.
4.1. Reverse DNS
With Reverse DNS validation the client proves control of an IP
address by provisioning a TXT resource record containing a designated
value for a specific validation domain name constructed using the
value of the PTR record for the reverse mapping of the address.
type (required, string): The string "reverse-dns-01".
token (required, string): A random value that uniquely identifies
the challenge. This value MUST have at least 128 bits of entropy,
in order to prevent an attacker from guessing it. It MUST NOT
contain any characters outside the base64url [RFC4648] alphabet,
including padding characters ("=").
GET /acme/authz/1234/2 HTTP/1.1
Host: example.com
HTTP/1.1 200 OK
{
"type": "reverse-dns-01",
"url": "https://example.com/acme/authz/1234/2",
"status": "pending",
"token": "evaGxfADs6pSRb2LAv9IZf17Dt3juxGJ-PCt92wr-oA"
}
A client responds to this challenge by constructing a key
authorization from the "token" value provided in the challenge and
the client's ACME account key. The client then computes the SHA-256
digest [FIPS180-4] of the key authorization. The record provisioned
to the authoritative DNS server is the base64url encoding of this
digest.
The client constructs the validation domain name by prepending the
label "_acme-challenge" to the domain name referenced in the PTR
resource record for the IN-ADDR.ARPA [RFC1034] or IP6.ARPA [RFC3596]
reverse mapping of the IP address. The client then provisions a TXT
record with the digest for this name.
For example, if the IP address being validated is 2001:db8::1 and its
IP6.ARPA mapping had the following PTR record:
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Internet-Draft ACME-IP March 2017
1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa. 300 IN PTR example.com
then the client would provision the following DNS record:
_acme-challenge.example.com. 300 IN TXT "gfj9Xq...Rg85nM"
The response to the Reverse DNS challenge provides the computed key
authorization to acknowledge that the client is ready to fulfill this
challenge.
keyAuthorization (required, string): The key authorization for this
challenge.
POST /acme/authz/1234/2
Host: example.com
Content-Type: application/jose+json
{
"protected": base64url({
"alg": "ES256",
"kid": "https://example.com/acme/acct/1",
"nonce": "JHb54aT_KTXBWQOzGYkt9A",
"url": "https://example.com/acme/authz/1234/2"
}),
"payload": base64url({
"keyAuthorization": "evaGxfADs...62jcerQ"
}),
"signature": "Q1bURgJoEslbD1c5...3pYdSMLio57mQNN4"
}
On receiving a response, the server MUST verify that the key
authorization in the response matches the "token" value in the
challenge and the client's ACME account key. If they do not match,
then the server MUST return an HTTP error in response to the POST
request in which the client sent the challenge.
To validate a DNS challenge, the server performs the following steps:
1. Compute the SHA-256 digest of the key authorization
2. Query for a PTR record for the IP identifiers relevant reverse
mapping based on its version
3. Query for TXT records for the computed validation domain name
4. Verify that the contents of one of the TXT records matches the
digest value
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Internet-Draft ACME-IP March 2017
If all of the above verifications succeed, then the validation is
successful. If no PTR or TXT DNS records are found, or the returned
TXT records do not contain the expected key authorization digest,
then the validation fails.
4.2. Existing Challenges
IP identifiers MAY be used with the existing "http-01" and "tls-sni-
02" challenges from RFC XXXX Sections XXX and XXX respectively. To
use IP identifiers with these challenges their initial DNS resolution
step MUST be skipped and the address used for validation MUST be the
value of the identifier.
The existing "dns-01" challenge MUST NOT be used to validate IP
identifiers.
5. IANA Considerations5.1. Identifier Types
Adds a new type to the Identifier list defined in Section XXX of RFC
XXXX with the label "ip" and reference RFC XXXX.
5.2. Challenge Types
Adds a new type to the Challenge list defined in Section XXX of RFC
XXXX with the label "reverse-dns-01", identifier type "ip", and
reference RFC XXXX.
Add the value "ip" to the identifier type column for the "http-01"
and "tls-sni-02" challenges.
6. Security Considerations6.1. Certificate Lifetime
Given the often short delegation periods for IP addresses provided by
various service providers CAs MAY want to impose shorter lifetimes
for certificates which contain IP identifiers. They MAY also impose
restrictions on IP identifiers which are in CIDRs known to be
assigned to service providers who dynamically assign addresses to
users for indeterminate periods of time.
7. Normative ReferencesShoemaker Expires September 28, 2017 [Page 5]